As shown in FIG. 1, the general heat treatment furnace has a single-plate or a double-plate feeding door on the exit, wherein the door plank is push-shifted to the lateral of the heat treatment furnace via pulleys. After shifting an object that waits for drying into the heat treatment furnace, the exit of the heat treatment furnace is closed and then heated for preforming the heat treatment process.
In accordance with the aforesaid door-open manner, the both sides of the exit of the heat treatment furnace must be vacated by a certain space so as to open or close the door plank normally. If the heat treatment furnace is huge in size, the vacated space on both sides of the exit of the heat treatment furnace must be correspondingly increased. As a result, it causes a waste of large space. In addition, the flexibility of configuring the overall space is thus reduced, and the factory rent cost is relatively increased.